Singapore is the largest bunkering port in the world and is trying to ensure that the business is conducted according to stringent rules to maintain it's reputation as a clean place in more ways then one.
Because of problems with cheating in the bunkering business in Singapore in the past, the rules governing the business has been strengthened several times in the last 10 years or so. First by requiring Bunker Surveyors to be given special training and being licensed by MPA. At the same time the punishment for cheating by suppliers and/or surveyors was strengthened and several operators banned from working within Singapore Port Limit: http://www.mpa.gov.sg/web/portal/home/port-of-singapore/port-operations/bunkering/bunkering-standards/singapore-standard-code-of-practice-for-bunkering-ss600
As the first bunkering port in the world, it is compulsory for all MFO bunkering operations to be done using a certified and calibrated Mass Flow Meter from 1. Jan. 2017: http://www.mpa.gov.sg/web/portal/home/port-of-singapore/circulars-and-notices/detail/pc14-08
Mass Flow Meters approved by MPA is supposed to be tamper free. They must be operated according to strict practisesc set by MPA: http://www.mpa.gov.sg/web/portal/home/port-of-singapore/port-operations/bunkering/bunkering-101-placards/mass-flow-metering-best-practices
The type of MFM used in Singapore is superior to those in use in the EU: http://www.mpa.gov.sg/web/portal/home/port-of-singapore/port-operations/bunkering/bunkering-101-placards/mass-flow-metering-best-practices
Old practises, like "frotting" as described above is no longer possible, but rest assure some enterprising bunker suppliers will try to find way of cheating, AND GET CAUGHT.